1. Field of the Invention
The present invention relates generally to a fixture designed to hold components together during a joining process. More particularly, the present invention relates to a magnetic fixture designed to hold the components of a housing enclosure of an electrochemical device or a medical device together during a joining process. In its broadest sense, however, the housing is a container comprising first and second parts that are joined together to form a closed container.
2. Description of Related Art
The sophistication and complexity of implantable medical devices continues to increase. As a result, these devices typically require additional electrical power to operate. In addition to the increased sophistication and complex capability, the size of these implantable medical devices is becoming increasingly smaller. Therefore, there is an increased need to manufacture electrochemical devices of increasing power and capability in a smaller volume in which to fit within and power these more compact and sophisticated medical devices.
Increasing the packaging efficiency is one approach to achieve improved electrical performance of electrochemical devices, such as electrochemical cells and capacitors, which power implantable medical devices. Improved electrical performance characteristics, such as energy density, electrical longevity, and electrical output of an electrochemical device can typically be improved through the maximized utilization of the interior space of the housing or enclosure of the electrochemical device. A more compact electrochemical device affords the ability to construct and power smaller medical devices which are less invasive to the patient without sacrificing therapeutic capability.
Electrochemical devices such as those used to power implantable medical devices, are typically constructed with a metallic housing comprised of two opposing case halves. During the manufacturing process, the active electrode materials, as well as other electrochemical device related components, are generally positioned within one half of the housing. A second housing portion, such as a corresponding enclosure half or enclosure lid, is mated to the first housing portion, thereby enclosing the electrochemical device therewithin. A weld is generally used to join these housing portions together. More specifically, a weld seam, extending circumferentially around the mating surfaces of the device, is used to create a hermetic seal therewithin. The integrity and robustness of this hermetic seal is of utmost importance in that the seal prevents the egress of body fluids within the cell and chemicals out of the cell. Migration of these fluids and chemicals could potentially harm the patient and/or damage the medical device within which the cell resides.
Because of the relatively compact size of these electrochemical devices, mating of the two opposing portions of the device housing requires exacting precision. Often, the opposing halves of the housing are manufactured to close dimensional tolerances, which increases the difficulty of joining the opposing sides of the housing. Therefore, there is a need to provide an improved means of joining the opposing housing portions of an electrochemical device together with improved precision. This is particularly critical in achieving an electrochemical device with a robust hermetic seal.
Furthermore, implantable medical devices, such as pacemakers, neurostimulators, defibrillators and the like, also generally comprise opposing housing portions. The joining of the housing portions of an implantable medical device, like the joining of the housing of an electrochemical device, as previously discussed, is also subject to similar manufacturing problems. Like the electrochemical device, the housing of the implantable medical device generally comprises two opposing metallic housing portions. The housing portions of the implantable medical device are also made to exacting dimensional tolerances, which increases the difficulty of precisely joining them together. Implantable medical devices are also being made to smaller dimensional sizes, therefore adding to the difficulty of joining the housing portions together.
Traditional welding fixtures generally comprise a mechanical restraint such as a clamp, strap, or the like that provides a mechanical means of holding the opposing fixture components together during the joining or welding process. The mechanical restraint of these prior art fixtures physically extends across the space between the left and right hand fixture components holding them together.
The housing portions, that are to be joined, are generally positioned within each of the respective left and right hand fixture components. The mechanical restraint is then positioned across the two fixture portions, securing the fixture together. However, the mechanical restraint, i.e., the clamp, strap or strut that physically extends across the space between the opposing fixture sides generally obstructs the line of sight of the joining or welding instrument. This obstruction is particularly problematic during a laser welding operation in which a laser beam is projected onto the joining surfaces. Such a fixture clamp could prevent the laser beam from contacting the surface behind the clamp, possibly resulting in a non-joined or partially joined portion.
In addition, fixture clamps further increase the difficulty of joining opposing housing portions wherein the welded pieces are rotated with respect to the laser beam. Furthermore, such obstructions inhibit the formation of a robust, hermetic seal that is formed completely around the perimeter of the housing of the device, whether the device is an electrochemical device or an implantable medical device.
As a result, elaborate fixtures have been developed to minimize blockage of the application of the laser welding beam to the weld surface. For example, fixtures have been developed which incorporate movable struts that are electronically controlled. When the laser beam approaches the clamp or strut, these struts are designed to move out of the way of the laser beam, thereby removing the obstruction. These fixtures require additional electronic components to coordinate such movement of the clamp or strut. In addition, these fixtures comprising movable components are prone to mechanical wear, alignment and timing issues, which increases manufacturing costs.
Furthermore, the relatively small size of the housing portions of these electrochemical and medical devices increases the difficulty with which to utilize these prior art welding fixtures. The relatively small size of these devices therefore, requires correspondingly small fixture components and subassemblies with intricate moving parts. Therefore, there is a need to provide an improved welding fixture that does not require the use of mechanical clamps to hold opposing portions of the fixture together during the welding process.
In addition, the increased packing efficiency and relatively small size of the device housing makes these electrochemical and medical devices prone to overheating during the welding process. Heat generated from the welding process, particularly heat generated from a laser beam, could transfer from the weld seam into the bulk of the device, thereby potentially damaging the chemicals or circuitry within the devices. For example, such heat provided by the welding process could warp the housing or damage the active electrochemical materials or associated device components. Therefore, there is a need to provide an improved means and apparatus thereof that minimizes heating during the joining of the housing of the electrochemical or medical device, particularly during a laser welding process.
Accordingly, the present invention provides an improved welding fixture that does not require the use of mechanical clamping. In addition, the fixture of the present invention provides for the precise mating of opposing housing or enclosure portions. Furthermore, the fixture of the present invention provides a heat sink that effectively diverts heat flow away from the weld area and components of the device therewithin.